The present invention relates to medical devices; in particular, the present invention provides devices and methods for sensing thickness of cardiac tissue and the like so that medical procedures may be efficiently performed through and/or upon a discrete location having suitable tissue thickness.
The present invention relates to dilation and/or ablation catheters for treatment of cardiac arrhythmia, for example atrial fibrillation. More particularly, it relates to a catheter configured for transseptal access to the left atrium so that a mapping and/or ablation catheter can be advanced into the left atrium. As is known in the art, an ablation catheter is used to electrically isolate a vessel, such as a pulmonary vein, from a chamber, such as the left atrium with a continuous lesion pattern and a method for forming such a lesion pattern.
The heart includes a number of pathways that are responsible for the propagation of signals necessary to produce continuous, synchronized contractions. Each contraction cycle begins in the right atrium where a sinoatral node initiates an electrical impulse. This impulse then spreads across the right atrium to the left atrium, stimulating the atria to contract. The chain reaction continues from the atria to the ventricles by passing through a pathway known as the atrioventricular (AV) node or junction, which acts as an electrical gateway to the ventricles. The AV junction delivers the signal to the ventricles while also slowing it, so the atria can relax before the ventricles contract.
Disturbances in the heart""s electrical system may lead to various rhythmic problems that can cause the heart to beat irregularly, too fast or too slow. Irregular heart beats, or arrhythmia, are caused by physiological or pathological disturbances in the discharge of electrical impulses from the sinoatrial node, in the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid depolarizations in the atrial muscles. These impulses can conduct to the ventricles causing potentially lethal ventricular arrhythmias. Patients experiencing atrial fibrillation may suffer from fatigue, activity intolerance, dizziness and even strokes.
The precise cause of atrial fibrillation, and in particular the depolarizing tissue causing xe2x80x9cextraxe2x80x9d electrical signals, is currently unknown. As to the location of the depolarizing tissue, it is generally agreed that the undesired electrical impulses often originate in the left atrial region of the heart. Recent studies have expanded upon this general understanding, suggesting that nearly 90% of these xe2x80x9cfocal triggersxe2x80x9d or electrical impulses are generated in one (or more) of the four pulmonary veins (PV) extending from the left atrium.
It has been postulated that this tissue may spontaneously depolarize, resulting in an unexpected electrical impulse(s) propagating into the left atrium and along the various electrical pathways of the heart. In this regard, as the heart develops from an embryotic stage, left atrium tissue may grow or extend a short distance into one or more of the PVs. In addition, during gestation an intra-atrial valve (i.e., the Fossa Ovalis valve) remains open and closes, or is rendered latent, following birth. The latent valve provides a relatively thin tissue location through which a catheter may advance for access to the left atrium. Unfortunately, the latent valve is difficult to locate using traditional means such as fluoroscopy.
A variety of different atrial fibrillation treatment techniques are available, including drugs, surgery, implants, and catheter ablation. While drugs may be the treatment of choice for some patients, drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually correct an arrhythmia only after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem by ablating the abnormal tissue or accessory pathway responsible for the atrial fibrillation thereby disrupting ionic conduction pathways of the abnormal tissue. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radio frequency (RF) electrical energy, laser energy, and the like. The energy source, such as an ablating electrode, is normally disposed along a distal portion of a catheter.
Most ablation catheter techniques employed to treat atrial fibrillation focus upon locating the ablating electrode, or a series of ablating electrodes, along extended target sections of the left atrium wall. Because the atrium wall, and thus the targeted site(s), is relatively tortuous, the resulting catheter design includes multiple curves, bends, extensions, etc. In response to recent studies indicating that the unexpected electrical impulses are generated within a PV, efforts have been made to ablate tissue within the PV itself. Obviously, the prior catheter designs incorporating convoluted, multiple bends are not conducive to placement within a PV. Instead, a conventional xe2x80x9cstraight endedxe2x80x9d ablation catheter has been employed. While this technique of tissue ablation directly within a PV has been performed with relatively high success, other concerns may arise.
More particularly, due to the relatively small thickness of atrial tissue formed within a PV, it is likely that ablation of this tissue may in fact cause the PV to shrink or constrict. Because PV""s have a relatively small diameter, a stenosis may result. Even further, other vital bodily structures are directly adjacent each PV. These structures may be undesirably damaged when ablating within a PV.
In light of the above, an alternative technique has been patented by Medtronic, Inc. whereby a continuous ablation lesion pattern is formed in the left atrium wall about the ostium associated with the PV in question. In other words, the PV is electrically isolated from the left atrium by forming an ablation lesion pattern that surrounds the PV ostium. As a result, any undesired electrical impulse generated within the PV could not propagate into the left atrium, thereby eliminating unexpected atria contraction. One exemplary patent related to the foregoing is U.S. Pat. No. 6,325,797 the contents of which are hereby incorporated by reference herein.
Unfortunately, while PV isolation via a continuous ablation lesion pattern about the PV ostium appears highly viable, no acceptable ablation catheter configuration exists. Most atrial fibrillation ablation catheters have linear distal ends, designed for manipulation in a sliding fashion along the atrial wall. That is to say, the distal, electrode-carrying end of the catheter is typically slid along (or parallel to) the atrial wall. With this generally accepted configuration in mind, it may be possible to shape the distal, electrode-carrying end into a small ring sized in accordance with the PV ostium. For example, U.S. Pat. No. 5,617,854 discloses one such possibility. More particularly, the described ablation catheter includes a substantially ring-shaped portion sized to contact the ostium of the coronary sinus. Pursuant to conventional designs, the ring extends linearly from the catheter body. In theory, the ringshaped portion may be placed about a PV ostium. However, proper positioning would be extremely difficult and time consuming. More particularly, it would be virtually impossible to locate and then align the ring about a PV ostium when sliding the catheter along the atrium wall. The ring must be directed toward the ostium in a radial direction (relative to a central axis of the ostium). Even if the electrophysiologist were able to direct the ring to the ostium, the periodic blood flow through the PV would likely force the ring away from the atrium wall, as the catheter body would not provide any support.
A related concern entails mapping of a PV prior to ablation. In cases of atrial fibrillation, it is necessary to identify the origination point of the undesired electrical impulses prior to ablation. Thus, it must first be determined if the electrical impulse originates within one or more PVs. Once the depolarizing tissue has been identified, necessary ablation steps can be taken. Mapping is normally accomplished by placing one or more mapping electrodes into contact with the tissue in question. In order to map tissue within a PV, therefore, a relatively straight catheter section maintaining two or more mapping electrodes must be extended axially within the PV. Ablation catheters configured to slide along the atrial wall cannot include a separate, distal extension for placement within the PV. Instead, an entirely separate mapping catheter must be provided and then removed for subsequent replacement with the ablation catheter. Obviously, these additional steps greatly increase the overall time required to complete the procedure.
Electrical isolation of a pulmonary vein via an ablation lesion pattern surrounding the pulmonary vein ostium presents a potentially revolutionary technique for treatment of atrial fibrillation. However, the unique anatomical characteristics of a pulmonary vein and left atrium render currently available ablation catheters minimally useful. Therefore, a substantial need exists for an ablation catheter designed for rapid and accurate identification of the latent Fossa Ovalis valve so that a suitable catheter may be advanced therethrough.
The present invention provides an improved apparatus for performing a septal puncture procedure and methods for fabricating and using same. In one form of the invention, a remotely deployable thickness sensing probe couples to a distal end of an elongated cardiac tissue dilator or cardiac tissue ablation apparatus and provides a signal related to relative tissue thickness adjacent the probe. The dilator or ablation apparatus is preferably resilient to axial compression and torque. To efficiently fabricate such apparatus low cost, non-imaging thickness sensing probes are preferred. Such probes may be electrically wired or may provide signals wirelessly to remote (i.e., external) medical monitoring equipment. The thickness sensing probe may comprise acoustic-type sensor probes (e.g., so-called ultrasound-, ultrasonic-types). Such probes transmit and receive (i.e., transceive) signals that penetrate a local region of tissue. The signals relate to the volume of tissue proximate the probe. The signals may be used to confirm location of a relatively thin portion of tissue suitable for temporarily being pierced during a medical procedure such as a cardiac procedure requiring transseptal access. While a unitary transceiver is desirable, separate transmitting and receiving units may be used.
In addition to the foregoing, the signals provided according to the present invention may also be used to determine how much ablation energy (e.g., radio frequency, laser, etc.) or where a surgical ablation apparatus should be applied to a surface, such an endocardial surface.
In practice, an apparatus according to the present invention is used to interrogate a tissue surface and provide signals relating to the thickness of a local region of the tissue. This information is then conveyed to a clinician. The information can be displayed on a monitor or other remote device, can be conveyed as an acoustic signal (e.g., varying pitch, tone or volume based on a sensed thickness parameter of tissue), and/or can be conveyed as a tactile response, and the like. A variety of tissue thicknesses may be interrogated; however, for the transseptal tissue of interest, a range of about 0.1 mm to approximately 10 mm is preferred. The magnitude and frequency of acoustic energy delivered the transducer should of course be designed as appropriate for a given tissue region.
With respect to axial compression and torque ranges for the elongated portion of the apparatus, a design similar to those current tissue dilators having a Brockenbrough needle coupled thereto is generally suitable for use in conjunction with the present invention. A marking or identification unit is preferably disposed on or near the distal end portion of the apparatus so that the orientation and location of the end portion may be viewed (e.g., using a fluoroscope and the like).
The region of tissue preferably comprises a latent Fossa Ovalis valve of a patient for a transseptal procedure. In such a procedure, a clinician advances the distal end of a catheter to the right atrium, and then probes for an appropriate region of reduced thickness to pierce to gain access to the left atrium. Since most humans have such a latent valve structure left over from gestation, this is a preferred route for accessing the left atrium so that left atrial chamber and the pulmonary valves therein may be accessed so that a variety of therapies may be applied thereto.